The retention of ammonia and sulfur dioxide during riming of ice particles and dendritic snow flakes: laboratory experiments in the Mainz vertical wind tunnel

Laboratory experiments were carried out in the Mainz vertical wind tunnel to determine the retention of the trace gases ammonia and sulfur dioxide dissolved in supercooled cloud droplets during riming. The conditions during riming were similar to the ones in atmospheric mixed phase clouds: temperatures from ?18 °C to ?5 °C, liquid water contents between 1 and 1.5 g m^?3, liquid drop radii between 10 and 20 μm, liquid phase concentrations from 1 to 22 mg/l. As collectors, floating ice particles and snow flakes with diameters between 6 mm and 1.5 cm were used. After riming the retention coefficients, i.e. the fractions of the species which remained in the ice phase after freezing were determined. Retention coefficients lying between 0.1 and 1.0 were measured depending on the solubility and dissociation of the trace gas, liquid phase concentration, ambient air temperature, and shape of rimed collector. This can be explained from the chemists’ point of view by the effective Henry’s law constant of the species and physically with the rate of latent heat removal from the rimed collector during freezing. Parameterizations derived from the different experimental cases describe the retention coefficients as a function of temperature. In general, an average retention of ammonia of 92?±?21 % was determined independently of liquid phase concentration while mean values for sulfur dioxide were 53?±?10 % at low liquid phase concentrations and 29?±?7 % at high liquid phase concentrations.     

Impact of climate variability on summer fires in a Mediterranean environment (northeastern Iberian Peninsula)

We analyse the impact of climate interannual variability on summer forest fires in Catalonia (northeastern Iberian Peninsula). The study period covers 25 years, from 1983 to 2007. During this period more than 16000 fire events were recorded and the total burned area was more than 240 kha, i.e. around 7.5% of whole Catalonia. We show that the interannual variability of summer fires is significantly correlated with summer precipitation and summer maximum temperature. In addition, fires are significantly related to antecedent climate conditions, showing positive correlation with lagged precipitation and negative correlation with lagged temperatures, both with a time lag of two years, and negative correlation with the minimum temperature in the spring of the same year. The interaction between antecedent climate conditions and fire variability highlights the importance of climate not only in regulating fuel flammability, but also fuel structure. On the basis of these results, we discuss a simple regression model that explains up to 76% of the variance of the Burned Area and up to 91% of the variance of the number of fires. This simple regression model produces reliable out-of-sample predictions of the impact of climate variability on summer forest fires and it could be used to estimate fire response to different climate change scenarios, assuming that climate-vegetation-humans-fire interactions will not change significantly.     

From accessing to assessing forecasts: an end-to-end study of participatory climate forecast dissemination in Burkina Faso (West Africa)

This study compares responses to seasonal climate forecasts conducted by farmers of three agro-ecological zones of Burkina Faso, including some who had attended local level workshops and others who had not attended the workshops. While local inequalities and social tensions contributed to excluding some groups, about two-thirds of non-participants interviewed received the forecast from the participants or through various means deployed by the project. Interviews revealed that almost all those who received the forecasts by some mechanism (workshop or other) shared them with others. The data show that participants were more likely to understand the probabilistic aspect of the forecasts and their limitations, to use the information in making management decisions and by a wider range of responses. These differences are shown to be statistically significant. Farmers evaluated the forecasts as accurate and useful in terms of both material and non-material considerations. These findings support the hypothesis that participatory workshops can play a positive role in the provision of effective climate services to African rural producers. However, this role must be assessed in the context of local dynamics of power, which shape information flows and response options. Participation must also be understood beyond single events (such as workshops) and be grounded in sustained interaction and commitments among stakeholders. The conclusion of this study point to lessons learned and critical insights on the role of participation in climate-based decision support systems for rural African communities.     

Low- and high-alumina komatiites of Goiás, Central Brazil

Archean komatiites of Goiás, central Brazil, have experienced deformation and low-grade metamorphism, but several outcrops preserve primary volcanic features. Samples from less deformed komatiites of four out of five greenstone belts (Crixás, Guarinos, Pilar de Goiás, and Santa Rita) have been investigated for their geochemical properties. Komatiites from the Crixás greenstone belt have very low Al₂O₃/TiO₂, high CaO/Al₂O₃, and a hump-shaped rare earth element (REE) pattern. Those from the Guarinos and Pilar de Goiás belts have similar REE patterns, characterized by a slight enrichment in LREE coupled with almost flat HREE, but differ in their inter-incompatible element ratios. Compared with those from Pilar de Goiás and Guarinos, samples from the Santa Rita belt have fractionated REE patterns with LREE enrichment, as well as high Al₂O₃ contents, corresponding to Al-undepleted komatiites. Komatiites from Crixás have the lowest (La/Sm)_N, (La/Yb)_N, and Zr/Zr* ratios compared with their equivalents from the other belts, which suggests their source was relatively depleted in LREE and high field strength elements (HFSE), probably due to the retention of garnet in the residue. Komatiites from the Guarinos, Pilar de Goiás, and Santa Rita greenstone belts are enriched in incompatible elements, which can be attributed to either low-degree partial melting at high pressures or a source previously enriched in incompatible elements. Some of the studied komatiites belong to Al- and HREE-depleted and others to the Al- and HREE-undepleted types. The depleted komatiites probably derived by melting at depths greater than 200 km, the undepleted at less than 200 km. Therefore, the komatiites of the four belts may have been derived from either one single mantle plume with different melting depths or sources from distinct plumes.     

High-resolution simulations of the last glacial maximum climate over Europe: a solution to discrepancies with continental palaeoclimatic reconstructions?

The analyses of low-resolution models simulations of the last glacial maximum (LGM, 21 kyr BP) climate have revealed a large discrepancy between all the models and pollen-based palaeoclimatic reconstructions. In general, the models are too warm relative to the observations, especially in winter, where the difference is of the order of 10°C over western Europe. One of the causes of this discrepancy may be related to the low spatial resolution of these models. To assess the impact of using high-resolution models on simulated climate sensitivity, we use three approaches to obtain high-resolution climate simulations over Europe: first an atmospheric general circulation model (AGCM) with a stretched grid over Europe, second a homogeneous T106 AGCM (high resolution everywhere on the globe) and last a limited area model (LAM) nested in a low-resolution AGCM. With all three methods, we have performed simulations of the European climate for present and LGM conditions, according to the experimental design recommended by the Palaeoclimate Modeling Intercomparison Project (PMIP). Model results have been compared with updated pollen-based palaeoclimatic indicators for temperature and precipitation that were initially developed in PMIP. For each model, a low-resolution global run was also performed. As expected, the low-resolution simulations underestimate the large cooling indicated by pollen data, especially in winter, despite revised slightly warmer reconstructions of the temperatures of the coldest month, and show results in the range of those obtained in PMIP with similar models. The two high-resolution AGCMs do not improve the temperature field and cannot account for the discrepancy between model results and data, especially in winter. However, they are able to reproduce trends in precipitation more closely than their low-resolution counterparts do, but the simulated climates are still not as arid as depicted by the data. Conversely, the LAM temperature results compare well with climate reconstructions in winter but the simulated hydrological cycle is not consistent with the data. Finally, these results are discussed in regard of other possible causes for discrepancies between models and palaeoclimatic reconstructions for the LGM European climate.     

A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin

Oligocene–Miocene chronostratigraphic correlations within the Paratethys domain are still highly controversial. This study focuses on the late Early Miocene of the Swiss and S-German Molasse Basin (Late Burdigalian, Ottnangian–Karpatian). Previous studies have published different chronologies for this time interval that is represented by the biostratigraphically well constrained Upper Marine Molasse (OMM, lower and middle Ottnangian), Upper Brackish Molasse (OBM, Grimmelfingen and Kirchberg Formations, middle and upper Ottnangian to lower Karpatian, MN 4a–MN 4b) and Upper Freshwater Molasse (OSM, Karpatian–Badenian, MN 5). Here, we suggest a new chronostratigraphic framework, based on integrated magneto-litho-biostratigraphic studies on four sections and three boreholes. Our data indicate that the OBM comprises chrons 5D.1r and 5Dn (Grimmelfingen Fm), chron 5Cr (lower Kirchberg Fm) and the oldest part of chron 5Cn.3n (upper Kirchberg Fm). The OSM begins during chron 5Cn.3n, continues through 5Cn, and includes a long reversed segment that can be correlated to chron 5Br. The OMM-OSM transition was completed at 16.0 Ma in the Swiss Molasse Basin, while the OBM-OSM changeover ended at 16.6 Ma in the S-German Molasse Basin. As the lower Kirchberg Fm represents a facies of the Ottnangian, our data suggest that the Ottnangian–Karpatian boundary in the Molasse Basin is approximately at 16.8 Ma, close to the 5Cr–5Cn.3n magnetic reversal, and thus 0.4 Myr younger than the inferred age of 17.2 Ma used in recent Paratethys time scales. Notably, this would not be problematic for the Paratethys stratigraphy, because chron 5Cr is mainly represented by a sedimentation gap in the Central Paratethys. We also realise, however, that additional data is still required to definitely solve the age debate concerning this intriguing time interval in the North Alpine Foreland Basin. We dedicate this work to our dear friend and colleague Jean-Pierre Berger (8 July 1956–18 January 2012).     

Alkyl nitrates and bifunctional nitrates of atmospheric interest: Henry's law constants and their temperature dependencies

Henry's law coefficients of 15 alkyl nitrates, keto-, hydroxy-, and dinitrates of atmospheric interest have been measured, mostly over the temperature range 1–25°C. The compounds are stable in aqueous solution. Where literature data were available, Henry's law coefficients are in very good agreement. It is concluded that dissolution in cloud and rain water is not an important loss process for alkyl mononitrates in the atmosphere. The residence times of the more soluble bifunctional organic nitrates, however, are significantly affected or even controlled by washout and rainout. Gas chromatographic analysis of bifunctional nitrates in preconcentrated atmospheric samples may be adversely affected by the adsorptive properties of these compounds.     

What can we learn from aerosol measurements at baseline stations?

In this paper the results of existing baseline aerosol monitoring programs are reviewed. For this purpose, aerosol data from five baseline stations in both hemispheres are analysed. Their information content is compared to that which can be derived when utilizing experiences of recent field experiments and the present state of aerosol sciences in general. Recommendations for extensions and reductions of baseline aerosol measurements are given.     

Diffusion of HTO,Br, I,Cs, Sr and Co in a clay formation: Results and modelling from an in situ experiment in Opalinus Clay

The migration of radioactive and chemical contaminants in clay materials and argillaceous host rocks is characterised by diffusion and retention processes. Valuable information on such processes can be gained by combining diffusion studies at laboratory scale with field migration tests. In this work, the outcome of a multi-tracer in situ migration test performed in the Opalinus Clay formation in the Mont Terri underground rock laboratory (Switzerland) is presented. Thus, 1.16 × 10⁵ Bq/L of HTO, 3.96 × 10³ Bq/L of ⁸⁵Sr, 6.29 × 10² Bq/L of ⁶⁰Co, 2.01 × 10⁻³ mol/L Cs, 9.10 × 10⁻⁴ mol/L I and 1.04 × 10⁻³ mol/L Br were injected into the borehole. The decrease of the radioisotope concentrations in the borehole was monitored using in situ γ-spectrometry. The other tracers were analyzed with state-of-the-art laboratory procedures after sampling of small water aliquots from the reservoir. The diffusion experiment was carried out over a period of one year after which the interval section was overcored and analyzed. Based on the experimental data from the tracer evolution in the borehole and the tracer profiles in the rock, the diffusion of tracers was modelled with the numerical code CRUNCH.     

Controls on carbonate platform architecture and reef recovery across the Palaeozoic to Mesozoic transition: A high-resolution analysis of the Great Bank of Guizhou

Carbonate platforms spanning intervals of global change provide an opportunity to identify causal links between the evolution of marine environment and depositional architecture. This study investigates the controls on platform geometry across the Palaeozoic to Mesozoic transition and yields new stratigraphic and palaeoenvironmental constraints on the Great Bank of Guizhou, a latest Permian to earliest Late Triassic isolated carbonate platform in the Nanpanjiang Basin of south China. Reconstruction of platform architecture was achieved by integrating field mapping, petrography, biostratigraphy, satellite imagery analysis and δ¹³C chemostratigraphy. In contrast to previous interpretations, this study indicates that: (i) the Great Bank of Guizhou transitioned during Early Triassic time from a low-relief bank to a platform with high relief above the basin floor (up to 600 m) and steep slope angles (preserved up to 50°); and (ii) the oldest-known platform-margin reef of the Mesozoic Era grew along steep, prograding clinoforms in an outer-margin to lower-slope environment. Increasing platform relief during Early Triassic time was caused by limited sediment delivery to the basin margin and a high rate of accommodation creation driven by Indosinian convergence. The steep upper Olenekian (upper Lower Triassic) slope is dominated by well-cemented grainstone, suggesting that high carbonate saturation states led to syndepositional or rapid post-depositional sediment stabilization. Latest Spathian reef initiation coincided with global cooling following Early Triassic global warmth. The first Triassic framework-building metazoans on the Great Bank of Guizhou were small calcareous sponges restricted to deeper water settings, but early Mesozoic reef builders were volumetrically dominated by Tubiphytes, a fossil genus of uncertain taxonomic affinity. In aggregate, the stratigraphic architecture of the Great Bank of Guizhou records sedimentary response to long-term environmental and biological recovery from the end-Permian mass extinction, highlighting the close connections among marine chemistry, marine ecosystems and carbonate depositional systems.